Vacuum tubes for generating electron beams have long been known, as the generation and acceleration of free electrons is favorably accomplished in a low pressure environment. For example, devices such as television picture tubes use accelerated electrons to excite points on a phosphorescent screen which thereafter irradiate light for viewing.
In order for electron beams to be produced in a vacuum tube for use outside the low pressure environment of the tube, windows have been developed which allow electrons to exit the tube but keep gases at ambient pressure from entering. Since a beam of electrons penetrating such a window can result in heating that destroys the window, means of cooling such windows have also been developed.
In U.S. Pat. No. 3,486,060, Swanson teaches the use of a number of angled orifices for directing laminar flow of cooling gases across a metal window. U.S. Pat. No. 3,562,793 to McCann et al. also teaches the use of laminar gas flow to externally cool metal windows for charged particles.
U.S. Pat. No. 3,629,576 to Enge describes a focussing electrode for use in an accelerator tube, the electrode generally shaped as a plate having a central aperture through which charged particles pass and a symmetric variation of indentations encircling that aperture.
In U.S. Pat. No. 3,702,973, Daugherty et al. describe a laser or ozone generator in which electrons generated by emission from filaments are accelerated to a plate held at positive potential, the plate having a plurality of holes that allow some electrons to pass through, the holes covered with a metal diaphragm through which some electrons penetrate to reach a gas such as oxygen. U.S. Pat. No. 3,883,413 to Douglas-Hamilton discloses the use of such a device with pulsed electron beams and decaying electric fields. In U.S. Pat. No. 4,095,115, Orr, Jr. et al. disclose a hollow cathode plasma discharge device utilizing a metal window and adjacent high velocity oxygen gas for producing ozone.
U.S. Pat. No. 4,409,511 to Loda et al. describes a phase transition cooling system for charged particle accelerators, the cooling system involving directing atomized, vaporizable liquid at charged particle windows made of metal or plastic. In U.S. Pat. No. 4,468,282, Neukermans teaches a method of making amorphous thin film windows for use with ink jet printers.
In U.S. Pat. No. 4,764,947, Lesensky teaches a cathode focussing arrangement for production of x-rays by electrons impinging upon a metal anode. U.S. Pat. No. 4,825,123 to Franzel et al. discloses a method for making x-ray tubes wherein a cathode cup is manufactured in two pieces to minimize damage to the cathode or filament.
U.S. Pat. No. 5,093,602 to Kelly teaches of a device for atomizing a stream of fluent material which can use an electron beam directed through an electron permeable membrane formed of amorphous boron-nitride to facilitate dispersion of a liquid. In U.S. Pat. No. 5,210,426, Itoh et al. teach of an electron beam device including an electron permeable window formed of a Ti-Al composite. Finally, U.S. Pat. No. 5,235,239 to Jacob et al. teaches of various foil window constructions for a particle accelerator.
A number of applications for which low voltage electron beams are particularly desirable creates a desire for further improvements in this area.